The present disclosure generally relates to operations conducted within a wellbore, and, more specifically, to methods for suppressing bacterial growth in a subterranean environment.
Treatment fluids can be used in a variety of subterranean operations. Such subterranean operations can include, without limitation, drilling operations, stimulation operations, production operations, remediation operations, sand control treatments and the like. As used herein, the terms “treat,” “treatment” and “treating” refer to any subterranean operation that uses a fluid in conjunction with achieving a desired function and/or for a desired purpose. Use of these terms does not imply any particular action by the treatment fluid or any component thereof, unless otherwise specified herein. Illustrative treatment operations can include, for example, fracturing operations, gravel packing operations, acidizing operations, scale dissolution and removal operations, consolidation operations, and the like.
A number of types of bacteria can be natively present in a subterranean formation, or they can be introduced into a subterranean formation in the course of drilling and completing a wellbore. The elevated temperatures of the subterranean environment can readily promote rapid bacterial growth. In addition, a number of treatment fluids contain materials that are ready food sources for some bacteria, which can further exacerbate bacterial growth issues.
Due to a number of undesirable consequences, it can often be desirable to suppress the propagation of bacteria within a subterranean environment and/or in a treatment fluid being introduced into a subterranean environment. Growth of bacterial colonies within a subterranean formation can produce sludge or slime within the formation and decrease the formation's porosity. Decreased porosity can lower production of a hydrocarbon resource from the formation. Sulfate-reducing bacteria can be particularly problematic within a subterranean environment, since they release hydrogen sulfide as a metabolic product. Hydrogen sulfide can result in corrosion of downhole metal goods, produce deleterious health effects, and lessen the quality of a produced hydrocarbon resource. When hydrogen sulfide or sulfur-containing organic compounds are present in a produced hydrocarbon resource, for example, costly refining techniques may be required in order to make the hydrocarbon resource suitable for its intended end use. Bacterial growth can also degrade certain components within a treatment fluid, such as viscosifying polymers, thereby changing the treatment fluid's properties and possibly making the treatment fluid unsuitable for its originally intended purpose.
Because of the serious consequences bacteria can produce in a subterranean environment, a number of techniques are used to suppress bacterial growth downhole. Continuous or pulsed ultraviolet light sources may be used for this purpose, but bacterial growth may resume if the bacteria are not all killed or inactivated by the light source. Similarly, chemical biocides may be used to suppress bacterial growth in a subterranean formation or in a treatment fluid. Although chemical biocides can be effective against various types of bacteria, it is often difficult to maintain the biocide in a desired location downhole. For example, chemical biocides can exit the subterranean environment during flowback of a treatment fluid, again allowing bacterial growth to resume if the bacteria are not all killed or inactivated. Chemical biocides can also be expensive and subject to decomposition in the harsh conditions of a subterranean environment. In addition, some chemical biocides can decompose the active components of a treatment fluid. For example, oxidative chemical biocides can decompose viscosifying polymers that are present in a fracturing fluid. There may also be environmental concerns associated with some chemical biocides.
Bacterial growth within the recesses of a subterranean formation can be particularly difficult to suppress. Specifically, it can be difficult to deliver a chemical biocide or an ultraviolet light treatment into inaccessible subterranean regions, such as the regions within and beyond propped fractures of a subterranean formation. In addition, conveying a chemical biocide through previously propped fractures can upset placement of the proppant, potentially undoing the effects of a fracturing operation and reducing the formation's permeability.